1. Field of the Invention
The present invention relates to a file management that uses one or more storage devices and optimally disposes files in accordance with the properties of a file system, in which file system snapshots are acquired.
2. Description of the Related Art
Currently, storage devices provided with various performances have been developed, and performances of volumes forming these storage devices are different from each other. Generally, a volume of high performance is expensive, and cannot have much capacity. On the other hand, a volume of low performance is inexpensive, and can have much capacity.
There is known a method for managing data referred to as the HSM function (Hierarchical Storage Management function) that optimally disposes files, in which a plurality of volumes of different properties are utilized to reduce the cost of storage. In the HSM function, the file system program migrates a frequently used file to a high-speed and expensive volume, and migrates an infrequently used file to a low-speed and inexpensive volume. In this way, the HSM function controls file-storing volumes, which can reduce the cost of storage.
The HSM function disclosed in a patent document 1 (US2004/0193760A1) creates a file system using a high-speed volume and a low-speed volume, in which a file system program sends an instruction to migrate an unutilized file to the low-speed volume. Then, when an application accesses the file, the file is migrated to the low-speed volume. In this processing, the file system rewrites file management information of the high-speed volume.
On the other hand, there is known the file system snapshot function (which may be simply referred to as snapshot function, hereinafter) which is disclosed in a patent document 2 (Japanese Laid-Open Patent Publication No. 2004-342050). The file system snapshot function can easily recover an original file when the user deletes the file or modifies the file by mistake. The file system snapshot function acquires a file system image of a specific time point like a “photograph (snapshot)”. The user can recover a file, which is deleted by mistake, by acquiring the file from the snapshot. The snapshot function has a special volume referred to as a “differential data volume” to store data of a deleted file or a modified file.
In the HSM function disclosed in the patent document 1, when supporting the file system snapshot function, a differential data volume is required for both a high-speed volume (LU (Logical Unit) created with FC (Fibre Channel) Disk) and a low-speed volume (LU created with SATA (Serial Advanced Technology Attachment) Disk). Accordingly, when supporting the snapshot function using a file system provided by the HSM function, a differential data volume of large amount is required.